Proceedings Paper

Optical fiber whitelight interferometers for distance measurement have attracted a lot of attention recently because they
offer absolute measurement, ultrahigh accuracy, large dynamic range, and robustness. In this paper, the development of
an in-fiber whitelight interferometric distance sensor based on the mode coupling effect of a long period fiber grating
(LPFG) is presented. Unlike the Fabry-Perot interferometric (FPI) distance sensor that has a minimum requirement on
the measurable distance, the LPFG-based distance sensor can measure a distance that is as small as several nanometers.
Therefore, it can be applied for near-field surface profiling of micro/nano-sized components. The principle of operation
of the LPFG-based distance sensor is first explained and an innovative micro-photolithographic technique to fabricate
the sensor probe is described in detail. The performance of the distance sensors using two different types of LPFGs,
laser-machined LPFG and mechanically induced LPFG, were evaluated and the experimental results are presented.